The present invention relates to the art of diagnostic imaging. It finds particular application in conjunction with magnetic resonance imaging and will be described with particular reference thereto. However, it is to be appreciated that the present invention may also find application in conjunction with CT scanners, nuclear cameras, and other electronic image reconstruction techniques.
Conventionally, magnetic resonance imagers have included a single receiving channel for receiving magnetic resonance signals for conversion into an image representation. Commonly, a single coil having a configuration particularly adapted to the region of the patient to be imaged is disposed within the bore of the magnetic resonance imager and interconnected with the receiver. In a quadrature detection system, the receiver includes a signal splitter which divides the magnetic resonance signal into sine and cosine components. The sine and cosine components are each demodulated to eliminate the carrier frequency and filtered to remove stray frequency components. One analog-to-digital converter digitizes the filtered sine component and a second converter digitizes the filter cosine component. A two dimensional Fourier transform computer subroutine transforms the digitized sine and cosine resonance signal data into phase maps or image representations.
One of the problems with the prior art magnetic resonance imagers resided in the relatively high noise of the receiver. Due to the range of experimental conditions such as pulse sequences, the small ratio of the peak of the zero phase encoded echo to its least discernable side lobe, and variable image parameters such as the field view and slice thickness, it is necessary for the receiver to handle a wide dynamic amplitude range of magnetic resonance signals. The receiver has to handle the largest anticipated signal without compression, yet also process the smallest anticipated signal.
In early magnetic resonance imagers, the lower signal-to-noise ratio of the magnetic resonance signal dominated the noise of the receiver and the analog-to-digital converters. However, due to higher field strengths and other improvements, the signal-to-noise ratio of the received magnetic resonance signal no longer necessarily dominates the noise of the receiver.
Using surface coils, imaging a plurality of body parts has heretofore required a corresponding plurality of scans. After each scan, the coil is moved adjacent a second body part and a second scan is conducted to generate the data for the image of the second body part. Alternately, the adjacent body parts could be imaged in one scan by increasing the size of the coil and the field of view. However, such an increase in the field of view increases the noise and lowers the resolution.
The present invention provides a new and improved magnetic resonance imaging technique and apparatus which overcomes the above referenced problems and others.